Fixed issue

MediaBrowser.MediaEncoding/Encoder/MediaEncoder.cs

@@ -903,9 +903,8 @@ namespace MediaBrowser.MediaEncoding.Encoder
             using (var processWrapper = new ProcessWrapper(process, this))
             {
                 bool ranToCompletion = false;
-
-                await _thumbnailResourcePool.WaitAsync(cancellationToken).ConfigureAwait(false);
-                try
+                
+                using (await _thumbnailResourcePool.LockAsync(cancellationToken).ConfigureAwait(false))
                 {
                     StartProcess(processWrapper);
 
@@ -959,10 +958,6 @@ namespace MediaBrowser.MediaEncoding.Encoder
                         StopProcess(processWrapper, 1000);
                     }
                 }
-                finally
-                {
-                    _thumbnailResourcePool.Release();
-                }
 
                 var exitCode = ranToCompletion ? processWrapper.ExitCode ?? 0 : -1;